/Engine/Source/Runtime/Engine/Classes/Animation/CustomAttributesRuntime.h
Add (negated) any new or subtract from existing custom attributes
static void SubtractAttributes ( const [UE::Anim::FStackAttributeContainer](API\Runtime\Engine\Animation\FStackAttributeContainer) & SourceAttributes, [UE::Anim::FStackAttributeContainer](API\Runtime\Engine\Animation\FStackAttributeContainer) & OutAttributes )